Room temperature high transparent niO thin film and preparation method thereof

Abstract

The application discloses a room-temperature high-transparency NiO film and a preparation method thereof. The method comprises the following steps: firstly, a gray initial NiO film containing multi-valence nickel defects is deposited on a transparent glass substrate by using a direct current magnetron sputtering; then, the film is immersed in a phosphate-citric acid-PEG-ascorbic acid composite reduction solution, and is treated at room temperature for 2.5-3.5 minutes; finally, the film is cleaned and dried. The composite reduction solution takes deionized water as a solvent, and is composed of the following components with the mass percentage: L-ascorbic acid 0.55%-0.65%, anhydrous disodium hydrogen phosphate 1.28%-1.48%, sodium dihydrogen phosphate dihydrate 0.62%-0.72%, citric acid monohydrate 0.09%-0.11%, and PEG400 2.5%-3.1%. The application can convert the gray low-transparency NiO film into a high-transparency pure-phase film at room temperature, and the prepared NiO film has an average transmittance of greater than or equal to 83% in the 380-760nm wavelength band, and the Ni content is reduced from 47.5% to 18.8%, and the binding force is maintained at level 1. + The application has the advantages of simple process, no high temperature, and suitability for rigid and flexible substrates.

Description

Technical Field

[0001] This invention relates to the field of functional thin film materials technology, and in particular to a room temperature high transparency NiO thin film and its preparation method. Background Technology

[0002] Nickel oxide (NiO), as an important p-type semiconductor material, has good chemical stability, electrochemical activity and optical modulation performance, and is widely used in optoelectronic devices such as smart windows, displays, and ultraviolet detectors.

[0003] Magnetron sputtering is one of the mainstream processes for preparing NiO thin films due to its advantages such as fast deposition rate, good film uniformity, high film quality, and ease of industrial mass production. However, when preparing NiO thin films by magnetron sputtering, the ratio of argon (Ar) to oxygen (O2) (hereinafter referred to as the argon-oxygen ratio) is a key parameter that determines the phase composition of the film, and its control precision directly affects the stoichiometry of the film.

[0004] Due to factors such as the flow rate stability of the argon-oxygen mixture, pressure fluctuations in the reaction chamber, and changes in the sputtering state of the target material during magnetron sputtering, the argon-oxygen ratio is difficult to control precisely. Furthermore, under certain non-ideal sputtering conditions, high-valence nickel defects (such as Ni) may also be generated in the thin film. 3+ These high-valence defects introduce light absorption centers, causing the NiO film to appear distinctly gray and significantly reducing its transmittance, making it difficult to meet the requirements of optoelectronic devices for highly transparent electrodes or active layers.

[0005] To address these issues, existing technologies often employ methods such as optimizing sputtering parameters (e.g., precisely controlling gas flow rate, stabilizing reaction chamber pressure) or subsequent heat treatment (e.g., high-temperature oxidation). However, the former requires extremely high equipment precision, increasing production equipment costs, and still struggles to completely prevent the formation of impurity phases; the latter requires additional high-temperature processing steps, which not only prolongs the production cycle but may also lead to cracking of the thin film structure or decreased adhesion to the substrate, while increasing energy consumption and production process complexity. Summary of the Invention

[0006] The purpose of this invention is to provide a simple, low-cost method for preparing NiO thin films that can efficiently eliminate high-valence defects, thereby overcoming the above-mentioned technical problems.

[0007] To achieve the above objectives, the solution of the present invention is: a method for preparing a room-temperature highly transparent NiO thin film, comprising the following steps: Magnetron sputtering deposition: An initial NiO thin film was deposited on a transparent glass substrate using a DC magnetron sputtering process; Liquid-phase treatment with composite reducing solution: The initial NiO film obtained above is completely immersed in the composite reducing solution and left to stand at 20~25°C for 2.5~3.5 min before being removed; the composite reducing solution uses deionized water as solvent and consists of the following components in the following mass percentages: L-ascorbic acid 0.55%~0.65%, anhydrous disodium hydrogen phosphate 1.28%~1.48%, sodium dihydrogen phosphate dihydrate 0.62%~0.72%, citric acid monohydrate 0.09%~0.11%, and PEG400 2.5%~3.1%; Post-treatment cleaning and drying: The NiO film after liquid phase treatment is cleaned with deionized water and dried to obtain a pure phase NiO film with a visible light transmittance of ≥80%.

[0008] As a preferred embodiment, the mass ratio of anhydrous disodium hydrogen phosphate, sodium dihydrogen phosphate dihydrate, and citric acid monohydrate in the composite reducing solution is 40:20:3.

[0009] As a preferred embodiment, the 30 mL composite reducing solution system is prepared as follows: 27.5 mL of deionized water is measured, and 0.40 g of anhydrous disodium hydrogen phosphate, 0.20 g of sodium dihydrogen phosphate dihydrate, 0.03 g of citric acid monohydrate, and 0.18 g of ascorbic acid (all solid components) are added sequentially. Then, 0.8 mL of PEG400 liquid is measured and added to the system, and the mixture is stirred at room temperature until completely dissolved.

[0010] As a preferred embodiment, the transparent glass substrate is a conductive glass substrate or an insulating glass substrate with an average transmittance of ≥83% in the visible light band.

[0011] As a preferred embodiment, before magnetron sputtering deposition, a pretreatment step for the transparent glass substrate is further included. The pretreatment includes: ultrasonically cleaning the transparent glass substrate sequentially with acetone, ethanol, and deionized water, each step lasting 14-16 minutes, followed by nitrogen drying; and placing the dried transparent glass substrate in a vacuum environment for desorption treatment at 20-25°C for 14-16 minutes.

[0012] As a preferred embodiment, the magnetron sputtering deposition includes the following steps: The pretreated transparent glass substrate is placed in the magnetron sputtering chamber, the reaction chamber is closed, and a vacuum of 2x10⁻¹ is drawn. -3 Pa; A nickel target with a purity of ≥99.99% was used as the sputtering target material, and the target-substrate distance was 6~10cm; A mixture of Ar and O2 gas is introduced, with an Ar flow rate of 20-60 sccm and an O2 flow rate of 5-20 sccm. The reaction chamber pressure is 0.2-1.5 Pa, the sputtering power is 60-180 W, and the deposition time is 10-30 min.

[0013] As a preferred embodiment, before introducing the Ar and O2 mixed gas for formal magnetron sputtering deposition, a pre-sputtering step is also included, which includes: pre-sputtering for 9 to 11 minutes under a pure argon atmosphere and a chamber pressure of 0.9 to 1.1 Pa.

[0014] As a preferred option, in the post-treatment cleaning and drying steps, the NiO film is immersed in ultrapure deionized water with a resistivity ≥18.5MΩ·cm and left to stand for 9~12 minutes at room temperature.

[0015] As a preferred option, in the post-treatment cleaning and drying steps, the cleaned NiO film is dried at room temperature in nitrogen at a constant flow rate of 3~8L / min.

[0016] A room-temperature high-transparency NiO thin film was prepared by the above method. The average transmittance of the NiO thin film in the visible light band of 380~760nm is ≥83%.

[0017] After adopting the above solution, the beneficial effects of the present invention are as follows: This invention utilizes a phosphate-citric acid-PEG-ascorbic acid composite reducing solution to perform liquid-phase treatment on the initial NiO thin film after magnetron sputtering. L-Ascorbic acid, as a mild reducing agent, can precisely remove Ni from the crystal lattice. 3+ High-priced defects reduced to stable Ni 2+ It eliminates light absorption centers caused by high-valence nickel, significantly improving the visible light transmittance of the film; citric acid acts as a complexing and solubilizing agent, accelerating the dissolution and removal of high-valence nickel; the phosphate system stabilizes the solution pH, making the reduction reaction more gentle and controllable, avoiding local over-reduction; PEG400 is used to improve the wettability and spreadability of the film surface, resulting in better processing uniformity and higher light transmittance consistency across the entire film; all components are prepared at room temperature without high-temperature processes, the reagents are inexpensive and environmentally friendly, and it is suitable for various substrates such as glass and flexible PET.

[0018] NiO prepared by magnetron sputtering 1-x In the thin film, Ni 3+ High-valence defects are the main strong light absorption centers; even trace amounts can cause the film to appear gray and significantly reduce transmittance. This invention utilizes the directional reduction effect of a composite reducing solution to reduce Ni in the crystal lattice. 3+ Efficiently converting Ni to a stable form 2+ This allows the film composition to approach a pure-phase NiO equilibrium, resulting in a significant improvement in transmittance.

[0019] XPS verification confirmed that the NiO thin film prepared by the method of this invention contains Ni. 3+ The content is 18.8%, which is higher than that of the initial NiO film. 3+The content was reduced by more than 60%. The average transmittance of this NiO film in the visible light band (380~760nm) can reach more than 83%, which meets the optical requirements of high-performance optoelectronic devices for transparent electrodes or active layers.

[0020] Furthermore, the entire process was completed at room temperature (20~25°C), which effectively avoided the risks of thermal stress, film cracking, and adhesion degradation caused by high temperatures. Cross-cut adhesion testing showed that the adhesion between the film and the substrate remained at the highest level (Level 1) after treatment, and the main NiO lattice was not damaged.

[0021] This invention requires no expensive or complex modifications to existing magnetron sputtering production lines, achieving the desired effect through a combination of standard sputtering processes and room-temperature liquid phase treatment. The reagents used are inexpensive, safe, and environmentally friendly. This method exhibits good adaptability to a variety of substrates, including glass and flexible polymers (such as PET). Attached Figure Description

[0022] Figure 1 This is a flowchart of the method for preparing the room temperature high transparency NiO thin film of the present invention.

[0023] Figure 2 These are the transmittance curves of the initial NiO film and the NiO film treated with the composite reduction solution in Example 1 of the present invention at wavelengths of 200~800nm.

[0024] Figure 3 The transmittance curves of the NiO thin film at wavelengths of 200-800 nm are obtained after parallel repeat experiments of Example 1 and Example 2 of the present invention.

[0025] Figure 4 This is the XPS spectrum of the NiO thin film after treatment with a composite reducing solution in Example 1 of the present invention.

[0026] Figure 5 This is the XPS spectrum of the initial NiO thin film in Example 1 of the present invention.

[0027] Figure 6 These are XPS spectra of NiO thin films after parallel repeat experiments of Example 1 and Example 2. Detailed Implementation

[0028] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] This invention provides a room-temperature high-transparency NiO thin film, and the preparation method of this room-temperature high-transparency NiO thin film includes the following steps (refer to the flowchart). Figure 1 ): S1. Substrate pretreatment: A transparent glass substrate is selected, which may be a conductive glass substrate, an insulating glass substrate, or other insulating / conductive glass substrates with an average transmittance of ≥83% in the visible light band.

[0030] The transparent glass substrate was subjected to multi-stage ultrasonic cleaning using acetone, anhydrous ethanol, and ultrapure deionized water with a resistivity ≥18.5 MΩ·cm in sequence, with each stage lasting 14~16 minutes. After cleaning, it was dried with high-purity nitrogen.

[0031] Then, vacuum desorption treatment is performed at room temperature (20-25°C) for 14-16 minutes to completely remove adsorbed water vapor and gas from the substrate pores, thereby improving the adhesion between the subsequently deposited film and the substrate.

[0032] S2, Magnetron sputtering deposition: The pretreated transparent glass substrate was placed in the magnetron sputtering chamber, the reaction chamber was closed, and a vacuum of 2x10⁻¹ was applied. -3 Pa.

[0033] A nickel target with a purity of ≥99.99% was used as the target material, and the target-substrate distance was 6~10cm; Pure Ar gas was introduced to stabilize the chamber pressure at 0.9~1.1 Pa, and the target material was activated and pre-sputtered for 9~11 minutes to remove surface contaminants.

[0034] Subsequently, a mixture of Ar and O2 gas was introduced, and the DC power supply was started. The reaction chamber pressure was controlled at 0.2~1.5 Pa, the sputtering power at 60~180 W, the Ar flow rate at 20~60 sccm, and the O2 flow rate at 5~20 sccm. Deposition was carried out for 10~30 min to obtain a gray initial NiO film with a thickness of 150~200 nm.

[0035] S3, Liquid phase treatment of composite reducing solution Prepare compound reducing solutions as needed and use immediately after preparation.

[0036] The composite reducing solution uses deionized water as a solvent and consists of the following components in the indicated mass percentages: L-ascorbic acid 0.55%–0.65%, anhydrous disodium hydrogen phosphate 1.28%–1.48%, sodium dihydrogen phosphate dihydrate 0.62%–0.72%, citric acid monohydrate 0.09%–0.11%, PEG400 2.5%–3.1%, with the balance being deionized water. The preparation method is as follows: Take ultrapure deionized water according to the specified proportions, and sequentially add anhydrous disodium hydrogen phosphate, sodium dihydrogen phosphate dihydrate, citric acid monohydrate, PEG400, and L-ascorbic acid. Stir at room temperature until all components are completely dissolved and the solution is clear and transparent.

[0037] The initial NiO film was completely immersed in the prepared composite reducing solution and allowed to stand at 20-25°C for 2.5-3.5 minutes before being removed. The film must be removed within a very short time, and subsequent cleaning treatment should be performed immediately after removal.

[0038] This composite reducing solution uses phosphate as a pH buffer system, citric acid as a co-complexing agent, PEG400 as a surface wetting and dispersing agent, and L-ascorbic acid as the main reducing agent. It can gently and selectively react with Ni³⁺ in the film. + High-valence defects undergo a directional reduction reaction, transforming them into Ni², which is highly water-soluble. + Ions detach from the solid phase. The resulting Ni²⁺ + The ions exist in aqueous solution as hydrated ions and complex salts. In subsequent cleaning steps, they can be quickly and thoroughly removed along with the reaction precursor impurities, eliminating light absorption and scattering centers.

[0039] S4. Post-treatment cleaning and drying The NiO film after liquid phase treatment was immediately removed and completely immersed in ultrapure deionized water with a resistivity ≥18.5 MΩ·cm. It was then allowed to stand and clean at room temperature for 9~12 min. During this period, two low-amplitude horizontal shakings were performed, each lasting 4~6 s, to ensure that the residual composite reduction solution and its reaction products on the film surface were completely removed, thus avoiding residual impurities from affecting the optical performance of the film.

[0040] The cleaned NiO film was placed in nitrogen gas and dried at room temperature with a constant flow rate of 3~8L / min to finally obtain a completely transparent NiO film.

[0041] Example 1 The method for preparing a room-temperature high-transparency NiO thin film in this embodiment includes the following steps: S1. Substrate pretreatment and deposition preparation: A square ITO conductive glass of 20mm×20mm×2.1mm was selected as the transparent glass substrate. Three cleaning media, namely acetone, ethanol and ultrapure deionized water with resistivity ≥18.5MΩ·cm, were used to perform ultrasonic cleaning on the transparent glass substrate in sequence. The cleaning time for each medium was 15 minutes.

[0042] The cleaned transparent glass substrate was dried with nitrogen and then vacuum desorbed at 20~25°C for 15 minutes.

[0043] S2, Magnetron sputtering deposition: The pretreated transparent glass substrate was placed in the magnetron sputtering chamber, the reaction chamber was closed, and a vacuum of 2x10⁻¹ was applied. -3 Pa.

[0044] A 99.99% pure nickel target was used as the target material, and the target-substrate distance was set to 8 cm. 30 sccm of Ar gas was introduced to stabilize the chamber pressure at 1.0 Pa, and pre-sputtering was performed for 10 minutes. Then, a mixture of Ar and O2 gas was introduced, with an argon-oxygen ratio of 30 sccm:10 sccm, and the pressure in the reaction chamber was stabilized at 0.5 Pa. Turn on the DC power supply, set the sputtering power to 120W, and the deposition time to 20min to obtain a gray initial NiO film with a thickness of 150~200nm.

[0045] XPS analysis revealed that in this gray initial NiO film, Ni... 3+ The content is 47.5%, and its transmittance curve is referenced. Figure 2 The blue curve in the image, the XPS graph, is as follows: Figure 5 As shown; S3, Liquid phase treatment of composite reducing solution Prepare the reducing solution according to the 30 mL standard system: Measure 27.5 mL of ultrapure deionized water, and add 0.40 g of anhydrous disodium hydrogen phosphate, 0.20 g of sodium dihydrogen phosphate dihydrate, 0.03 g of citric acid monohydrate, and 0.18 g of L-ascorbic acid (all solid components) in sequence. Then measure 0.8 mL of PEG400 liquid and add it to the system. Stir at room temperature until completely dissolved. The mass fraction of each component in the formulation of this embodiment falls within the scope of the claims.

[0046] The initial NiO film was completely immersed in the composite reduction solution and left to stand for 3 minutes at 20-25°C.

[0047] S4. Post-treatment cleaning and drying After the NiO film was removed from the composite reduction solution, it was immediately placed in ultrapure deionized water with a resistivity ≥18.5 MΩ·cm and allowed to stand for 10 minutes. During this period, it was subjected to two low-amplitude horizontal shaking movements, each lasting 4-6 seconds.

[0048] The cleaned NiO film was placed in a nitrogen dryer and dried at a constant flow rate of 5L / min at room temperature to obtain a completely transparent NiO film.

[0049] S5, Performance Testing The transparent NiO thin film prepared above was subjected to the following performance tests: In terms of optical performance, this NiO film achieved an average transmittance of 83.7% in the visible light band, as shown in the reference transmittance curve. Figure 2 The red curve in the image.

[0050] XPS analysis revealed that the key impurity Ni in the thin film... 3+The content is approximately 18.8%, indicating that most of the high-valence defects have been removed, and the film has achieved a high transmittance, as shown in its XPS spectrum. Figure 4 As shown.

[0051] Regarding structural and mechanical stability, the adhesion between the NiO film and the substrate was tested using the cross-cut test. The results showed that there was no detachment after the cross-cut test, and the adhesion level reached the highest level of 1, proving that the selective treatment of the composite reducing solution did not damage the film structure.

[0052] Furthermore, after being placed in a normal temperature and humidity environment for 1000 hours, the transmittance of the film did not change significantly, demonstrating good environmental chemical stability.

[0053] Example 2 This embodiment is a parallel replication of Example 1. The only difference between this embodiment and Example 1 is that the entire preparation process described above is independently repeated to verify the stability of the process.

[0054] Performance test results: Tests showed that the NiO film achieved an average transmittance of 83.81% in the visible light band. The transmittance curve is shown below. Figure 3 The blue curve in the image; Ni in the thin film 3+ The content is only 18.2%, and its XPS spectrum is as follows: Figure 6 As shown in the figure. The results above are basically consistent with those of Example 1, demonstrating that the method of the present invention has good reproducibility.

[0055] Comparative Example 1: No liquid phase treatment performed This comparative example provides a NiO thin film whose preparation method differs from that of the examples in that the initial NiO thin film is not treated with a composite reduction solution and washed with deionized water, but is directly subjected to performance testing.

[0056] Test results show that the film is dark gray, with an average transmittance of only 62.51% in the visible light band, as indicated by the reference transmittance curve. Figure 2 The blue curve in the image.

[0057] XPS analysis revealed that the Ni content in the initial NiO film was... 3+ The content is 47.5%. This indicates that the magnetron sputtering process itself easily generates a large number of high-valence impurity phases, severely impairing the transparency of the film. Without impurity removal treatment, optically pure NiO films cannot be obtained, and their XPS spectra are as follows. Figure 5 As shown.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the design of this case. All equivalent changes made based on the key design features of this case shall fall within the protection scope of this case.

Claims

1. A method for preparing a room-temperature highly transparent NiO thin film, characterized in that, Includes the following steps: Magnetron sputtering deposition: An initial NiO thin film was deposited on a transparent glass substrate using a DC magnetron sputtering process; Liquid phase treatment with composite reducing solution: The initial NiO film obtained above is completely immersed in the composite reducing solution and left to stand at 20~25°C for 2.5~3.5 min before being removed; the composite reducing solution uses deionized water as solvent and is composed of the following components in the following mass percentages: L-ascorbic acid 0.55%~0.65%, anhydrous disodium hydrogen phosphate 1.28%~1.48%, sodium dihydrogen phosphate dihydrate 0.62%~0.72%, citric acid monohydrate 0.09%~0.11%, PEG400 2.5%~3.1%, with the balance being deionized water; Post-treatment cleaning and drying: The NiO film after liquid phase treatment is cleaned with deionized water and dried to obtain a NiO film with a visible light transmittance of ≥80%.

2. The method for preparing a room-temperature highly transparent NiO thin film as described in claim 1, characterized in that: In the composite reducing solution, the mass ratio of anhydrous disodium hydrogen phosphate, sodium dihydrogen phosphate dihydrate, and citric acid monohydrate is 40:20:

3.

3. The method for preparing a room-temperature highly transparent NiO thin film as described in claim 1, characterized in that: The method for preparing the 30 mL composite reducing solution system is as follows: Measure 27.5 mL of deionized water, and add 0.40 g of anhydrous disodium hydrogen phosphate, 0.20 g of sodium dihydrogen phosphate dihydrate, 0.03 g of citric acid monohydrate, 0.8 mL of PEG400 and 0.18 g of ascorbic acid in sequence, and stir until completely dissolved.

4. The method for preparing a room-temperature high-transparency NiO thin film as described in claim 1, characterized in that: The transparent glass substrate is a conductive glass substrate or an insulating glass substrate with an average transmittance of ≥83% in the visible light band.

5. The method for preparing a room-temperature highly transparent NiO thin film as described in claim 1, characterized in that: Before magnetron sputtering deposition, a pretreatment step for the transparent glass substrate is also included. The pretreatment includes: ultrasonically cleaning the transparent glass substrate sequentially with acetone, ethanol and deionized water, each step lasting 14 to 16 minutes, and then drying it with nitrogen; placing the dried transparent glass substrate in a vacuum environment and desorbing it at 20 to 25°C for 14 to 16 minutes.

6. The method for preparing a room-temperature highly transparent NiO thin film as described in claim 1, characterized in that: The magnetron sputtering deposition includes the following steps: The pretreated transparent glass substrate is placed in the magnetron sputtering chamber, the reaction chamber is closed, and a vacuum of 2x10⁻¹ is applied. -3 Pa; A nickel target with a purity of ≥99.99% was used as the sputtering target material, and the target-substrate distance was 6~10cm; A mixture of Ar and O2 gas is introduced, with an Ar flow rate of 20-60 sccm and an O2 flow rate of 5-20 sccm. The reaction chamber pressure is 0.2-1.5 Pa, the sputtering power is 60-180 W, and the deposition time is 10-30 min.

7. The method for preparing a room-temperature highly transparent NiO thin film as described in claim 6, characterized in that: Before the formal magnetron sputtering deposition, a pre-sputtering step is included, which includes: pre-sputtering for 9 to 11 minutes under a pure argon atmosphere and a chamber pressure of 0.9 to 1.1 Pa.

8. The method for preparing a room-temperature highly transparent NiO thin film as described in claim 1, characterized in that: In the post-treatment cleaning and drying steps, the NiO film is immersed in ultrapure deionized water with a resistivity ≥18.5MΩ·cm and left to stand for 9~12 minutes at room temperature.

9. The method for preparing a room-temperature highly transparent NiO thin film as described in claim 1, characterized in that: In the post-treatment cleaning and drying steps, the cleaned NiO film is dried at room temperature in nitrogen at a constant flow rate of 3~8L / min.

10. A room-temperature high-transparency NiO thin film, characterized in that: The NiO film prepared by the method described in any one of claims 1 to 9 has an average transmittance of ≥83% in the visible light band of 380 to 760 nm.

Images